The functions of a computer-assisted surgery (CAS) system may include pre-operative planning of a procedure, presenting pre-operative diagnostic information and images in useful formats, presenting status information about a procedure as it takes place, and enhancing performance. The CAS system may be used for procedures in traditional operating rooms, interventional radiology suites, mobile operating rooms or outpatient clinics. Many approaches to CAS have been attempted commercially. The procedure may be any medical procedure, whether surgical or non-surgical.
Navigation systems are used to display the positions of surgical tools with respect to pre- or intraoperative image datasets. These images include intraoperative images, such as two-dimensional fluoroscopic images, and preoperative three dimensional images generated using, for example, magnetic resonance imaging (MRI), computer tomography (CT) and positron emission tomography (PET). The most popular navigation systems make use of a tracking or localizing system. These systems locate markers attached or fixed to an object, such as an instrument or a patient, and track the position of markers. These tracking systems are optical and magnetic, but also include acoustic systems. Optical systems have a stationary stereo camera pair that observes passive reflective markers or active infrared LEDs attached to the tracked tools. Magnetic systems have a stationary field generator that emits a magnetic field that is sensed by small coils integrated into the tracked tools. These systems are sensitive to nearby metal objects.
While navigation systems are relatively easy to integrate into the operating room, a fundamental limitation is that they have restricted means of communication with the surgeon. Most systems transmit information to the surgeon via a computer monitor. Conversely, the surgeon transmits information to the system via a keyboard and mouse, touchscreen, voice commands, control pendant, or foot pedals, and also by moving the tracked tool. The visual displays of navigation systems may at best display multiple slices through three-dimensional diagnostic image datasets, which are not easy to interpret for complex 3-D geometries. These displays also require the surgeon to focus his visual attention away from the surgical field.
When defining a plan using a tracked tool, it can be difficult to simultaneously position the tool appropriately in multiple degrees of freedom (DOFs). Similarly, when aligning a tracked instrument with a plan, it is difficult to control the position of the tool in multiple simultaneous DOFs, especially where high-accuracy is desirable. It is perhaps not a coincidence that navigation systems have had their largest acceptance in cranial neurosurgery, where most applications involve specifying a trajectory to a feature of interest without hitting critical features. Often, the tip of the tool is pressed against the anatomy and pivoted, effectively decoupling the position and orientation planning of the trajectory.
Autonomous robots have been applied commercially to joint replacement procedures. These systems make precise bone resections, improving implant fit and placement relative to techniques that rely on manual instruments. Registration is performed by having the robot touch fiducial markers screwed into the bones or a series of points on the bone surfaces. Cutting is performed autonomously with a high-speed burr, although the surgeon can monitor progress and interrupt it if necessary. Bones must be clamped in place during registration and cutting, and are monitored for motion, which then requires re-registration. Deficiencies reported by users of these systems include the large size of the robot, poor ergonomics, the need for rigidly clamping the bone for the 45–60 minutes required for registration and cutting, and the need for increasing the incision by 50–100 mm to provide adequate access for the robot. Furthermore, autonomous robots generally function best in highly structured environments, as evidenced by the rigid clamping of the bones of interest and making larger incisions to keep soft tissue away from the robot.
Except for specific steps of some surgical procedures, modern surgeries do not tend to provide well-structured environments for autonomous robots. A robot is generally not able to keep track of the surgical staff and instrumentation required to support a procedure. Although strict management of the operating environment might make this possible, the complexity of the human body will always provide a high degree of unstructuredness.
Robotic technology can also be used to improve upon standard practice without requiring autonomous operation. Notable commercial systems of this type include teleoperated robotic systems for laproscopic surgeries ranging from gall-bladder removal to closed-chest beating heart coronary surgery. These systems provide a console for the surgeon that includes a high-fidelity display and a master input device. The slave robot is coupled to the master and physically interacts with the anatomy. The benefits of these systems are primarily in providing an ergonomic working environment for the surgeon while improving dexterity through motion scaling and tremor reduction. Although the master console would normally be in the same room as the patient, an interesting byproduct of these systems is that they enable telesurgery. However, the robots have minimal autonomy in these systems, which is not surprising given the complexity involved in manipulating and altering soft tissue.